Seven Romanian children – some as young as nine – were found being forced to work as farm labourers in near-freezing conditions in Worcester last week, The Independent on Sunday has learned.

The children were among 50 Romanian workers discovered picking spring onions in a field in the Kempsey area of Worcester by the Gangmaster's Licensing Authority (GLA). The seven children, aged between nine and 15, were being made to work from 7.30 in the morning until dusk, dressed in thin summer clothes, as temperatures dropped close to zero.

Wellington boots that looked suitable for a five-year-old were also found in the field, suggesting even younger children had worked there. Investigators for the GLA say it is the first time they have come across such young children working in fields in the UK.

They were brought to the field in the back of a box van, with no food or water for the day. Six of the children have been taken into local authority care. Some were working alongside parents, but others appeared to have been brought to the farm on their own.

The workers said they were not sure how much they would be paid, but intelligence suggests that a household of up to 40 people would get no more than £100 a week for the job. The GLA, West Mercia Police and the UK Border Agency are still investigating and plan to arrest at least one unlicensed gangmaster this week.

Paul Whitehouse, chairman of the GLA, said: "In 2007 we celebrated the 200th anniversary of the end of the slave trade, but in 2010 we've got people working in appalling conditions who, while not actually being slaves, are very close to it."

The actress Juliet Stevenson is one of many leading figures supporting the IoS's campaign for an end to modern slavery and human trafficking, describing them as "the worst manifestation of human cruelty".

The actress said: "If it doesn't concern people that someone can be hijacked, kidnapped and manipulated away from their homes and families into horrendous situations that are at best hardship and at worst physical and mental brutality, then what does concern people?"

Stevenson said victims of trafficking who managed to escape their tormenters in Britain often have to go through a second ordeal at the hands of immigration authorities. "If you're not discovered you have to endure ongoing hell, but if you are discovered and thrown into an increasingly ruthless and unjust asylum system then you're also damned."

"Human trafficking represents just about the worst manifestation of human cruelty. If you're talking about the 'great' in Great Britain, let's look at having some moral leadership."

The Government faces calls from a growing number of high-profile campaigners to sign up to the EU directive on human trafficking, which would make it easier to prosecute traffickers and protect victims. Caroline Lucas MP, leader of the Green Party, and Yvette Cooper MP, Shadow Foreign Secretary and Minister for Women, have joined those demanding that the Government opt into EU trafficking legislation. There were signs that the Government feels compelled to respond to pressure to sign up to the directive. Simon Hughes MP, deputy leader of the Liberal Democrats, said last night: "Signing up to the EU directive has not been ruled out; it is under consideration by the Government."

The GLA is still waiting to hear the size of the cuts it can expect following the Comprehensive Spending Review. The authority is funded by the Department for Environment, Food and Rural Affairs, which faces budget cuts of 29 per cent.

Voices for change

"It's appalling that, in the 21st century, slavery still exists. That's why the Government must back Europe-wide action against trafficking. By pandering to anti-European prejudices in some parts of the Conservative Party, ministers are putting the safety of thousands of women and children at risk."

Yvette Cooper MP, Shadow Foreign Secretary and Women's Minister

"It seems a no-brainer. I oppose modern slavery like I oppose ancient slavery. Where's the argument? It's like saying 'should we care if someone is killed'."

Joan Bakewell, Broadcaster

"It's definitely a hidden problem because we think of slavery as being abolished. When I hear about modern slavery I tend to think of the Arab princes that bring their own staff and treat them abominably."

Alexei Sayle, Comedian, actor and author

"Wilberforce described slavery as 'a disgrace and a dishonour to this country', and I'd say exactly the same about the coalition's decision to opt out of the EU directive on human trafficking. I've signed this petition on behalf of the Green Party because Greens will always be on the side of people who are vulnerable, oppressed or abused."

Caroline Lucas MP, Leader, Green Party

"I'm astonished that we are so limp in this business. We know it's going on but we don't do anything about it. It's a moral principle. If we go back to Wilberforce, all the moral arguments against slavery were established then and we shouldn't go back on them by neglect."

Brian Sewell, Art critic

"For too long sex slavery and other forms of trafficking have been brushed under the carpet. The Archbishop of Canterbury said sex trafficking is a form of modern-day slavery and it is vital it becomes a public policy issue. The Independent on Sunday's campaign is vital in raising the profile of this issue. It's a shame that David Cameron and William Hague's Euro-scepticism is preventing the UK signing up to the EU directive to protect these people, but I also feel the police should name and shame the people who create the demand."

Denis MacShane, Rotherham MP and former Europe minister

"It's important because it's the thin end of the wedge. So many people rely on the minimum wage so if that's being eroded it can affect a lot of people."

Barry Cryer, Writer and comedian

Interviews by Joe Rowley

Join the IoS campaign

The Independent on Sunday is campaigning to persuade the Government to sign up to the EU directive on human trafficking. The directive will strengthen our laws to protect victims and make it easier to prosecute those who enslave them. Readers can call on David Cameron and Nick Clegg to do the right thing by signing the petition on the campaigning website 38 Degrees.